Allow video codec preference when publishing with RTCRtpEncodingParameters.

As per Lei's request, codec preference is a mandatory feature for simulcast.
This parameter is a workaround for setting video codecs. We'll move to
RTCRtpSendParameters in the future.

Author: jianjunz

src/sdk/base/publication.js

@@ -181,14 +181,14 @@ export class PublishOptions {
      * @member {?Array<Owt.Base.AudioEncodingParameters> | ?Array<RTCRtpEncodingParameters>} audio
      * @instance
      * @memberof Owt.Base.PublishOptions
-     * @desc Parameters for audio RtpSender.
+     * @desc Parameters for audio RtpSender. Publishing with RTCRtpEncodingParameters is an experimental feature. It is subject to change.
      */
     this.audio = audio;
     /**
      * @member {?Array<Owt.Base.VideoEncodingParameters> | ?Array<RTCRtpEncodingParameters>} video
      * @instance
      * @memberof Owt.Base.PublishOptions
-     * @desc Parameters for video RtpSender.
+     * @desc Parameters for video RtpSender. Publishing with RTCRtpEncodingParameters is an experimental feature. It is subject to change.
      */
     this.video = video;
   }

src/sdk/conference/channel.js

@@ -34,6 +34,7 @@ export class ConferencePeerConnectionChannel extends EventDispatcher {
     super();
     this._config = config;
     this._options = null;
+    this._videoCodecs = undefined;
     this._signaling = signaling;
     this._pc = null;
     this._internalId = null; // It's publication ID or subscription ID.
@@ -75,7 +76,7 @@ export class ConferencePeerConnectionChannel extends EventDispatcher {
     }
   }
 
-  publish(stream, options) {
+  publish(stream, options, videoCodecs) {
     if (options === undefined) {
       options = {audio: !!stream.mediaStream.getAudioTracks().length, video: !!stream
           .mediaStream.getVideoTracks().length};
@@ -218,6 +219,7 @@ export class ConferencePeerConnectionChannel extends EventDispatcher {
           };
           if (this._isRtpEncodingParameters(options.video)) {
             transceiverInit.sendEncodings = options.video;
+            this._videoCodecs = videoCodecs;
           }
           this._pc.addTransceiver(stream.mediaStream.getVideoTracks()[0],
             transceiverInit);
@@ -675,6 +677,11 @@ export class ConferencePeerConnectionChannel extends EventDispatcher {
   }
 
   _setRtpReceiverOptions(sdp, options) {
+    // _videoCodecs is a workaround for setting video codecs. It will be moved to RTCRtpSendParameters.
+    if (this._isRtpEncodingParameters(options.video) && this._videoCodecs) {
+      sdp = SdpUtils.reorderCodecs(sdp, 'video', this._videoCodecs);
+      return sdp;
+    }
     if (this._isRtpEncodingParameters(options.audio) ||
         this._isRtpEncodingParameters(options.video)) {
       return sdp;

src/sdk/conference/client.js

@@ -394,9 +394,10 @@ export const ConferenceClient = function(config, signalingImpl) {
    * @desc Publish a LocalStream to conference server. Other participants will be able to subscribe this stream when it is successfully published.
    * @param {Owt.Base.LocalStream} stream The stream to be published.
    * @param {Owt.Base.PublishOptions} options Options for publication.
+   * @param {string[]} videoCodecs Video codec names for publishing. Valid values are 'VP8', 'VP9' and 'H264'. This parameter only valid when options.video is RTCRtpEncodingParameters. Publishing with RTCRtpEncodingParameters is an experimental feature. This parameter is subject to change.
    * @returns {Promise<Publication, Error>} Returned promise will be resolved with a newly created Publication once specific stream is successfully published, or rejected with a newly created Error if stream is invalid or options cannot be satisfied. Successfully published means PeerConnection is established and server is able to process media data.
    */
-  this.publish = function(stream, options) {
+  this.publish = function(stream, options, videoCodecs) {
     if (!(stream instanceof StreamModule.LocalStream)) {
       return Promise.reject(new ConferenceError('Invalid stream.'));
     }
@@ -405,7 +406,7 @@ export const ConferenceClient = function(config, signalingImpl) {
           'Cannot publish a published stream.'));
     }
     const channel = createPeerConnectionChannel();
-    return channel.publish(stream, options);
+    return channel.publish(stream, options, videoCodecs);
   };
 
   /**